Method of operating a steam generator and improved burner system therefor



June 3, 1969 o. SCHWARZ ETAL 3,447,494

METHOD OF OPERATING A STEAM GENERATOR AND IMPROVED BURNER SYSTEM THEREFOR Filed 001;. 4, 1966 Sheet of 2 COaI/ Wafer Slurry IN VEN TORS OTTMAR SCHWARZ HEINRICH MERTEN Attorney June 1969 .SCHWARZ ETAL 3,447,494

METHOD OF OPERATING A STEAM GENERATOR AND IMPROVED BURNER SYSTEM THEREFOR Filed Oct. 4, 1966 Sheet 2 of 2 ML T 1 b Me F 3 Coal/Wafer {2/4 Slurry so I g c F -----fi I AB O +'-C0a//Wafer Slurry m I 0 Sfeam Generafor B c INVENTORS Rorary-cup Burn OTTMAR SCHWARZ FB HEINRICH MERTEN Attorney Fig. 4 BY United States Patent 3,447,494 METHOD OF OPERATING A STEAM GENERATOR AND IMPROVED BURNER SYSTEM THEREFOR Ottmar Schwarz, Ratingen, and Heinrich Merten, Essen,

Germany, assignors to Bergwerksverband GmbH, Essen- Kray, Germany, a corporation of Germany Filed Oct. 4, 1966, Ser. No. 584,217 Claims priority, application Germany, Oct. 7, 1965, B 84,025; June 10, 1966, B 87,503 Int. Cl. F23b 1/02; F23c 1/12; F23d 17/00 US. 'Cl. 110-7 13 Claims ABSTRACT OF THE DISCLOSURE A steam generator burner system and method of operating same in which a rotary atomizing cup receives a coal/water slurry containing 50 to 60% solids and disperses the fuel while combustion air is mixed with the dispersed fuel and, preferably pulverized coal is added to the combustion air.

Our present invention relates to burner arrangements for the fire boxes of installation and plants such as steam generators for heating a fluid destined to constitute the motivating fluid for a prime mover, a heating fluid or the like; more particularly, this invention relates to a method for operating a steam generator or other heating installation as well as to an improved bu-rner arrangement for such installation using coal/water suspensions as the fuel component.

Burner arrangements for industrial (furnaces, steam generators or the like have increasingly depended upon atomizable liquid fuels which are injected together with at least a primary air stream from a nozzle arrangement into the fire box or combustion chamber of the heating installation, the combustion-sustaining air being thoroughly mixed with the liquid fuel to atomize the latter or otherwise disperse it in a gaseous vehicle. The burners thus include atomizing nozzles for liquid fuels such as petroleum fractions, crude oil or refined oils as Well as solid fuels distributed in a liquid vehicle. More specifically, it has already been found to be advantageous to fire steam generators and other heating installations with a combustible coal/ air mixture in which the coal particles are finely divided and substantially uniformly dispersed in air so that an optimum heat value is obtained and relatively low grades of coal can be used without difliculty. The pulverized coal is generally produced in pulverizing apparatus although coal/water suspensions, with a solids content of 50 to 60% by weight are commonly used to facilitate transportation of the coal. Coal burners using puverized coal in admixture with a liquid vehicle have hitherto been primarily of the recirculation type wherein the combustible mixture is combined with exhaust gases so as to exploit the sensible heat thereof and increase the efiiciency of combustion and the fuel utilization. Apart from this system, however, it has been generally found that the solids content of the coal suspension prevented most other techniques used for improving the efficiency and fuel utilization of fuel oils from being applied to coal/water suspensions and burner installations therefor.

It is, therefore, the principal object of the present invention to provide an improved burner arrangement for coal/liquid suspensions which will both improve the fuel utilization and the combustion efficiency, While reducing the uncombusted content of the exhaust gases, will increase the effective combustion temperature and Will reduce the fuel consumption per unit of heat obtained.

Another object of this invention is to provide an im- 3,447,494 Patented June 3, 1969 proved method of operating a heating installation, such as a steam generator, whereby the heating efiiciency and fuel utilization can be markedly improved while the fuel con sists of a coal/ water suspension.

We have, surprisingly, discovered that, although most expedients designed to improve the fuel and combustion efiiciency of liquid petroleum or petroleum-fraction burners were totally ineffective when used with coal/ Water suspensions, a strikingly significant increase in fuel efficiency and utilization, improved in the cleaniness of combustion and the degree thereof, and reduction in the fuel quantity required per unit of thermal energy obtained when the coal/water suspension is atomized or dispersed with a rotaryacup burner into which the slurry is injected surrounded by an annular sheath of combustion air.

We have discovered most surprisingly, therefore, that coal-water slurries and suspensions having a solids content of 50-60 weight-percent can be burned completely and unobjectionably with efiiciencies approaching those of petroleum fuels when a rotary atomizing burner having a distributing cup open into the combustion chamber and having its discharge edge surrounded by an annular air nozzle is rotated at speeds of, say, 5000 to 6000 rpm. about its axis. Apparently, this unexpected improvement in the combustion efiiciency of the coal/water suspension is due in part to the intersecting flow of the finely divided or atomized fuel particles and the surrounding air stream at the discharge edge of the rotary cup. The burner, according to the invention, thus includes a distributor disposed axially rearwardly of the rotary cup which is open forwardly into the combustion chamber of the heating installation and supplies the coal/water suspension to this cup. The latter is advantageously mounted upon an axially extending shaft driven at a location remote from the burner head which forms a cylindrical sleeve extending substantially to the discharge edge of the cup but circumferentially spaced therefrom to form an air nozzle around this cup. A blower or other air-displacement means is connected with the duct formed by this sleeve for forcing a high-velocity air stream therethrough. The results obtainable with the present invention are all the more surprising when it is recognized that the sudden expansion of solid-in-liquid suspensions beyond a nozzle and at high velocity might normally be expected to sediment the solid particles from the vehicle in agglomerate form as this is a common principle in systems for the recovery of solids from liquid suspension thereof.

In the present system, however, it appears that there is no sedimentation, possibly because the high-velocity cup so co-operates with the surrounding jet of air as to assure complete and homogeneous dispersion of the solid in the fuel partticles ejected from this cup. Moreover, we have discovered that the high-velocity rotation of the atomizing cup leads to the induction of a central stream of hot exhaust or combustion gases from the fire box into the cup where it subjects the film of coal/water suspension to a preheating and drying step.

There is evidence that this induced contact of hot exhaust gas or burning gases from the fire chamber with the coal/water suspension serves to vaporize the water vehicle and leave the finely distributed coal in such a state of division that its combustion is accomplished rapidly and completely with a maximum of heat output. Furthermore, the steam produced in this manner appears to react with any coal residue in accordance with the Water-gas reaction (C+H O CO+H to produce hydrogen and carbon monoxide which are combustible and have excellent heat values. Thus, even if some sedimentation occurs, the water-gas reaction within the fire box cleanly removes such sedimentation and precludes contamination of the fire box or fuel Waste.

Accordingly to another feature of this invention, the burner arrangement for the industrial heating installation can be operated at low capacity or during starting by injecting into the combustion chamber a pulverized-coal/ air suspension via the annular air nozzle surrounding the rotary cup. The coal/ air suspension is then prepared from the coal/water slurry in a throughflow dryer of any conventional type.

It has been found that advantage in the present invention lies not only in enabling the use of a coal/water slurry having a high solids content (50-60 weight-percent solids) but also in that the system can be operated at partial load or as an auxiliary system if desired.

The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is an axial cross-sectional view of a rotarycup atomizer for the combustion of pulverized-coal/water slurries in accordance with the present invention;

FIG. 2 is an end view taken in the direction of arrow 11 of FIG. 1;

FIG. 3 is an axial cross-sectional view of another rotary-cup burner falling within the scope of this invention; and

FIG. 4 is a diagram illustrating certain aspects of the present method.

In FIG. 1, we show a burner assembly for the combustion of a pulverized-coal/Water suspension or slurry and adapted to open at its mouth (left-hand side of FIG. 1) into the burner chamber or fire box of an industrial heating installation such as a steam generator. The burner comprises essentially a distributing heat 1 which opens into a rotary cup 2 over the lip or edge 3 of which the fuel is injected in a finely divided state into the furnace chamber. The rotary cup 2 is surrounded by a casing 4a whose interior forms a duct 4 for the combustion air and is connected to a blower 4b as represented by the dotdash line 40. The forward end of the duct 4a frustoconcially tapers inwardly at 4d and is coaxial with the cup 2 so as to form an annular air nozzle 4e circumferentially surrounding the outwardly flared discharge edge 3 of the cup.

The rotary cup 2 is carried by a shaft 5 which, in turn, is driven by a motor 5a as represented diagrammatically in FIG. 1 at a minimum rate of, say 5000 to 6000 revolutions per minute. At this end, the distributing head 1 includes a hub 1a connected with the rotary cup 2 and having a central box 1b rotatably entrained with the shaft 5 via a key held in place by a screw head 10! threaded into the forward end of shaft 5. The hub member 1a thus forms a distributing chamber 7 of cup-like configuration which communicates with the interior of the rotary cup 2 via radial bores 8 open in the direction of wall 2a of this cup. The bores 8 are substantially uniformly distributed about the axis 5b of rotation of the shaft 5 and the cup 2. The head 1 also includes a duct 6 leading through the conduit 4a and carrying the pulverized-coal/ water slurry which is fed to the burner via a pump 6a. The slurry itself may be used as delivered from a fuelsupply source or may be prepared at the plant by combining pulverized coal with water as may be convenient for handling. The duct 6 has an extension 1e opening axially into the cup-shaped chamber 7 rearwardly of the rotary cup 2 and having radial bores 1f axially offset from the bores 8 but adapted to deliver the coal/water slurry to the chamber 7.

The rotary cup 2 flares slightly outwardly in the axial direction and thus is of frustoconical configuration with a widening mouth turned toward the combustion chamber. As the fuel dispersion flows in the direction of arrows 10 over the discharge edge 3 of the rotary cup 2, it is intersected by the annular jet of combustion air (arrows 1001) so that an intensive crossflow mixing of the fuel and combustion air is effected immediately in front of the mouth of the burner. As will be described in greater detail with reference to FIG. 3, the air channel 4 and nozzle 4e may be used to inject air-entrained pulverized coal into the combustion chamber to supplement the fuel supplied by the rotary cup 2 or in place thereof when the burner is operated at partially capacity. As best seen from FIG. 2, a stream of burning and/or hot exhaust gases is drawn inwardly along the axis of the burner (arrow 10b) and deflected outwardly along the wall 2a of the cup 2, thereby subjecting the fuel suspension to a partial drying and heating action. To facilitate the induction of gases and promote recirculation, we have found it to be advantageous to provide the interior of the cup 2 with scoop-like vanes 9a and 9b adapted to expedite axial intake and radial discharge of gases.

In the embodiment of FIG. 3, which operates in principle as described in connection with FIGS. 1 and 2, the distributing head 101 again forms a hub for the rotary cup 102 to which it is affixed at its 'base 101g. A key 1010 'held in place by a threaded nozzle 123 serves to rotatably entrain the cup 102 with the shaft 105. The latter is, of course, coupled with a motor as diagrammatically represented at 105a. The cup 102 diverges conically outwardly to its flared discharge lip 103. The rotary cup 102 again surrounded by a casing 104a whose duct 104 opens at an annular clearance 104:: to discharge air from a blower 104b land a line 1040 in crossflow to the fuel mixture emerging from the cup 102 at the hp 103. The latter is turned outwardy such that the fuel flow and air flows are at substantially right angles at the mouth of the burner.

The distributing head 101 is here subdivided axially into an outer compartment 107a and an inner compartment 107b to which extensions 101e and 101e' of respective ducts and 116 open. A compartment 107a opens via radial ports 108 into the interior of the cup 102. The latter is, however, surrounded with annular clearance .by the outer cup portion 117 so as to define an outer 'atomizing and accelerating cup 10% opening at 118 close to the lip 103. Radial bores 108a communicate between the distributing head 101 and its inner compartment 107k and this annular clearance 10%. Communication is permitted between compartments 107a and 107b so that if excess slurry is supplied via line 116 to the inner compartment 107b, it can overflow to compartment 107a and vice versa. This compartment thus has two outwardly flared distributing lips 103 and 118 both of which are surrounded by an annular clearance 104a supplying primary combustion air to the system. Each of the ducts 115 and 116 is supplied at a predetermined or variable rate with the coal/water slurry vi-a respective pumps 106a: and 1015b. The cup 102 with its outer cup portion 117 is here also driven at a minimum speed of, say, 5000 to 6000 rpm. The forward end of the duct 104a is provided with a support ring 120 into which the nozzle ring 121 is threaded so that the clearance defined at 104e and the location thereof can be adjusted upon rotation of this ring 121. The ring 121 carries a plurality of angularly spaced guide blades 121a for imparting a rotary movement to the emerging air about the axis of the burner, the blades 121a being inclined in the same sense with reference to axial planes of the burner.

According to a feature of this invention, the shaft 105 can be made tubular and formed with an axially extending how 122 which opens at anatomizing nozzle 123 coaxial with the cup 102 and terminating upstream of the mouth of the cup. A coal/water slurry, fuel oil or combustible gas :or air alone or admixed with these fuel substances can be supplied to the bore 122 via a pump 122a land a control valve 122b whereby the velocity of the jet 1220 emerging from the nozzle 123 can be controlled to regulate the toroidal vortex 123a formed thereby. This vortex counteracts the influx of burning gases and thereby permits the degree of recirculation to the burner to be carefully controlled and stabilized. An improved mixture of the combustible and burning gases is thereby insured.

In FIG. 4, we diagrammatically show a steam generator SG having a fire box FB into which 'a burner B of the type illustrated in FIG. 1 or FIG. 3 opens. Accord ing to this invention, the motor M drives the rotary cup of this burner at a speed of at least 5000 to 6000 rpm. while duct D delivers the coal/water slurry from a pump C to the rotary cup. A blower AB supplies the primary combustion air to the outer duct of the burner. A through fiow dryer SD can be supplied via another pump C with the coal/water slurry and can be heated by the exhaust gases from the steam generator as represented by the feedback line F. The dry pulverized coal can be combined with air at a mixer M in front of the blower AB when it is desired to supply the pulverized coal to the outer duct 4 or 104 of the burner. According to this invention, therefore, the burner can operate successively in a starting :mode, a normal operating mode and :an enlarged capacity mode as follows: during starting, there is substantially no recirculation of burning or exhaust gases to the mouth of the burner to facilitate the combustion and dispersion of the coal/water slurry. Accordingly, the slurry is not supplied to the rotary cup or is supplied in a minute quantity thereto whereas the major part of the starting fuel proportion is made up of diverted slurry, converted to pulverized coal in dryer SD, and supplied via the blower AB and mixer MA to the air duct of the rotary cup burner. As heat is built up in the system, the proportion of the diverted slurry is continuously or intermittently reduced until the coal/ water slurry is all introduced via the rotary cup and no further fuel is supplied through the air nozzle. During this latter phase of the operation of the burner, a substantially direct combustion of a coal/ water slurry is carried out. When it is necessary to augment the heat output of the burner, the supply of coal/water slurry is continued at maximum rate to the rotary cup or cups while additional slurry is converted to an air/coal suspension in the dryer DS and is supplied by the block AB to the air nozzle of the burner. When the burner of FIG. 3 is employed, one or more of the ducts 115, 116 may be used to supply the slurry depending upon the combustion requirements. When a partition is provided between the compartments 107a and 107b, the present invention contemplates supplying the coal/water slurry to the rotary cup 102 and an air/coal suspension (prepared as previously described) to the outer cup 102b. Additional pulverized coal can 'be supplied with the air .at 104 or the latter nozzle can be employed merely for combustion air. Fuel oil, air or combustible gases may be injected via nozzle 103 to control the recirculation of burning components within the chamber as mentioned earlier.

The invention described and illustrated is believed to 'admit of many modifications within the ability of persons skilled in the art, all such modifications being considered within the spirit and scope of the appended claims.

We claim:

1. A burner system comprising an axially open rotary atomizing cup having a divergent discharge edge at its open end; drive means for rotating said cup about an axis; distributing means communicating with said cup at a location remote from said end for supplying a fuel component thereto; means for delivering a coal/Water slurry to said distributing means as said fuel component; and means forming a nozzle surrounding said rotary cup at said edge for passing combustion air in crossfiow to the fuel component dispersed by said cup at said edge.

2. A method of operating a burner system wherein a burner supplies fuel and combustion air to a combustion chamber, said method comprising the steps of:

(a) atomizing a fuel component consisting essentially of a solid fuel suspended in a liquid and in the form of a coal/water slurry containing between substantially 50 and 60% by weight solids by introducing said component into a rotary-cup atomizer opening into said combustion chamber, and driving said rotary-cup atomizer at a rate sufiicient to disperse said fuel component;

(b) admixing the dispersed fuel component emerging from said rotary-cup atomizer with combustion air by supplying combustion air to said chamber from a nozzle surrounding said rotary-cup atomizer; and

(c) supplying through said nozzle to said combustion chamber pulverized coal entrained with said combustion air.

3. The method defined in claim 2 wherein pulverized coal and air are introduced through said nozzle during starting operation of said burner when the amount of said slurry supplied to said rotary-cup atomizer is minimal, said pulverized coal being formed by drying a coal/ water slurry.

4. The method defined in claim 2 wherein said pulverized coal is supplied to said nozzle during maximum flow of said slurry to said rotary-cup atomizer to augment the heat output of said burner, said pulverized coal being formed by drying a coal/ water slurry.

5. The method defined in claim 2 wherein said rotarycup atomizer is driven at a speed of at least 5000 revolutions per minute.

6. A method of operating a burner system wherein a burner supplies fuel and combustion air to a combustion chamber, said method comprising the steps of (a) atomizing a fuel component consisting essentially of a solid fuel suspended in a liquid and in the form of a coal/water slurry containing between substantially 50 and 60% by weight solids by introducing said component into a rotary-cup atomizer opening into said combustion chamber, and driving said rotary-cup atomizer at a rate sufiicient to disperse said fuel component;

(b) admixing the dispersed fuel component emerging from said rotary-cup atomizer with combustion air by supplying combustion air to said chamber from a nozzle surrounding said rotary-cup atomizer; and

(c) feeding a stream of fluid axially through said rotary-cup atomizer concurrently with the dispersion of said slurry thereby to regulate the recirculation of gases from said chamber into said rotary-cup atomizer.

7. The method defined in claim 6 wherein said rotarycup atomizer is driven at a speed of at least 5000 revolutions per minute.

8. A burner system comprising an axially open rotary atomizing cup having a divergent discharge edge at its open end; drive means for rotating said cup about an axis; distributing means communicating with said cup at a loaction remote from said end for supplying a fuel component thereto; means for delivering a coal/water slurry to said distributing means as said fuel component; means forming a nozzle surrounding said rotary cup at said edge for passing combustion air in cross-flow to the fuel component dispersed by said cup at said edge; and means for drying the coal/ air suspension supplied to said nozzle.

9. A burner system comprising an axially open rotary atomizing cup having a divergent discharge edge at its open end; drive means for rotating said cup about an axis; distributing means communicating with said cup at a location remote from said end for supplying a fuel component thereto; means for delivering a coal/water slurry to said distributing means as said fuel component; means forming a nozzle surrounding said rotary cup at said edge for passing combustion air in crossflow to the fuel component dispersed by said cup at said edge; and vane means in the interior of said cup for promoting the induction of gases from a region forwardly of said end into said cup and into intimate contact with said fuel component therein.

10. A burner system comprising an axially open rotary atomizing cup having a divergent discharge edge at its open end; drive means for rotating said cup about an axis; distributing means communicating with said cup at a location remote from said end for supplying a fuel component thereto; means for delivering a coal/Water slurry to said distributing means as said fuel component; means forming a nozzle surrounding said rotary cup at said edge for passing combustion air in crossfiow to the fuel component dispersed by said cup at said edge; and a rotarycup portion surrounding said rotary cup and forming an annular clearance therewith opening at said edge, said distributing means communicating with said annular clearance to supply a portion of said fuel component thereto.

11. A burner system comprising an axially open rotary atomizing cup having a divergent discharge edge at its open end; drive means for rotating said cup about an axis; distributing means communicating with said cup at a location remote from said end for supplying a fuel component thereto; means for delivering a coal/water slurry to said distributing means as said fuel component; means forming a nozzle surrounding said rotary cup at said edge for passing combustion air in crossfloW to the fuel component dispersed by said cup at said edge; and guide means in said nozzle for inducing a rotary movement of said combustion air about said axis upon its emergence from said nozzle.

12. A burner system comprising an axially open rotary atomizing cup having a divergent discharge edge at its open end; drive means for rotating said cup about an axis; distributing means communicating with said cup at a location remote from said end for supplying a fuel component thereto; means for delivering a coal/Water slurry to said distributing means as said fuel component; means forming a nozzle surrounding said rotary cup at said edge for passing combustion air in crossflow to the fuel component dispersed by said cup at said edge; and means for injecting a stream of fluid centrally through said cup for regulating the recirculation of gases into said cup from a region in front of the open end thereof.

13. A burner as defined in claim 12 wherein the lastmentioned means includes an atomizing nozzle coaxial with said cup.

References Cited UNITED STATES PATENTS 1,726,870 9/ 1929 Trent.

1,878,926 9/ 1932 Yarrow.

1,892,053 12/ 1932 Heaton.

1,953,090 4/1934 Vroom.

2,197,647 4/ 1940 Lorenzen.

3,124,086 3/1964 Sage et al 7 3,229,650 1/ 1966 Reichl.

CHARLES I. MYI- IRE, Primary Examiner.

US. Cl. X.R. 1l0--28; 431-168 

